diff --git a/open-sse/handlers/sseParser.ts b/open-sse/handlers/sseParser.ts
index 4a9626ac7b..aa579010bc 100644
--- a/open-sse/handlers/sseParser.ts
+++ b/open-sse/handlers/sseParser.ts
@@ -98,12 +98,14 @@ export function parseSSEToOpenAIResponse(rawSSE, fallbackModel) {
     }
   }
 
+  const joinedContent = contentParts.length > 0 ? contentParts.join("").trim() : null;
+  const joinedReasoning = reasoningParts.length > 0 ? reasoningParts.join("").trim() : null;
   const message: Record<string, unknown> = {
     role: "assistant",
-    content: contentParts.length > 0 ? contentParts.join("") : null,
+    content: joinedContent || null,
   };
-  if (reasoningParts.length > 0) {
-    message.reasoning_content = reasoningParts.join("");
+  if (joinedReasoning) {
+    message.reasoning_content = joinedReasoning;
   }
 
   const finalToolCalls = [...accumulatedToolCalls.values()].filter(Boolean).sort((a, b) => {
diff --git a/open-sse/utils/streamPayloadCollector.ts b/open-sse/utils/streamPayloadCollector.ts
index 427770fa08..58a20cbb5e 100644
--- a/open-sse/utils/streamPayloadCollector.ts
+++ b/open-sse/utils/streamPayloadCollector.ts
@@ -207,12 +207,14 @@ function buildOpenAISummary(events: StructuredSSEEvent[], fallbackModel?: string
     }
   }
 
+  const joinedContent = contentParts.length > 0 ? contentParts.join("").trim() : null;
+  const joinedReasoning = reasoningParts.length > 0 ? reasoningParts.join("").trim() : null;
   const message: JsonRecord = {
     role: "assistant",
-    content: contentParts.length > 0 ? contentParts.join("") : null,
+    content: joinedContent || null,
   };
-  if (reasoningParts.length > 0) {
-    message.reasoning_content = reasoningParts.join("");
+  if (joinedReasoning) {
+    message.reasoning_content = joinedReasoning;
   }
 
   const finalToolCalls = [...toolCalls.values()].sort((a, b) => a.index - b.index);